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NOVA: Extreme Ice | Ice-Core Record of Climate

In this video excerpt from NOVA: "Extreme Ice," learn about the historical record of climate changes captured in ice. Scientist Jim White discusses how ice cores store information about global climate and how scientists can study them. Graphs constructed from ice-core data illustrate the correlation between increases in greenhouse gases (such as carbon dioxide) and rises in global temperatures and sea levels. In the past, a major warming event caused a portion of Greenland's ice sheet to melt and raise sea levels. The recent ice-core record shows that as a result of the burning of fossil fuels, current levels of greenhouse gases are the highest they have been in the last half-million years, potentially putting Greenland's ice sheet in danger of melting more quickly than before.

This video is available in both English and Spanish audio, along with corresponding closed captions.

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A history of climate is recorded in glacial ice. Glaciers form as layers of snow accumulate on top of each other. Over time, the buried snow compresses under the weight of the snow above it, forming ice. Particulates that were captured by falling snow become a part of the ice, as do bubbles of trapped air. Layers of ice accumulate over seasons and years, storing information about the climate conditions at the time of formation (including precipitation, temperature, chemical composition of the atmosphere, volcanic eruptions, and solar activity). Scientists can study cores of glacial ice to learn about Earth's climate history. For example, scientists can measure the concentration of atmospheric gases in the bubbles of air and infer average temperatures through analysis of the ratio of oxygen isotopes.

Ice cores are cylinders of ice that are extracted from glaciers and ice sheets using hollow drill bits. Layers in the ice correspond to seasons or years, with the oldest ice at the bottom of the core and the youngest ice at the top. The ice-core record provides a natural time line of climate history. The National Ice Core Laboratory (NICL), a joint facility operated by the U.S. Geological Survey and the National Science Foundation, is the primary repository of ice cores in the United States. Located in Lakewood, Colorado, it houses over 45,000 feet (14,000 meters) of ice cores taken from locations in Greenland, Antarctica, and North America. The samples of ice are stored in a carefully temperature-controlled environment to ensure the integrity of the cores for current and future scientific investigations.

Using ice cores, scientists have constructed a history of climate extending back about 800,000 years. Ice cores show evidence of long cold periods interspersed with shorter warm periods; these natural climate variations are likely related to changes in Earth's orbit around the Sun. However, Earth's average temperature has risen at an alarming rate of about 1.4 degrees Fahrenheit (0.8 degrees Celsius) over the past century. The ice-core record shows that Earth's climate varies naturally and that it has gone through a number of warming and cooling trends in the past; however, it also indicates that the current warming is human induced. Scientists have found that there is a positive correlation between rising levels of greenhouse gases (such as carbon dioxide and methane) and global temperatures. The magnitude and rate of the abrupt recent increase in greenhouse gas levels, as well as the geochemistry of the carbon in the ice-core record, suggest it is caused by human activity—in particular, the burning of fossil fuels, which has greatly increased since the Industrial Revolution. The rapid temperature increase over the past century could cause portions of Greenland's ice sheet to melt faster than they have during previous warming events.

Here are some of the main ideas students should take away from this video:

Ice cores are like time capsules—they provide a history of climate that can date back hundreds of thousands of years. For example, the thickness of a layer of ice can provide information about how much snow fell that year. In addition, bubbles of trapped air allow scientists to measure past levels of carbon dioxide, methane, or nitrous oxide.

The National Ice Core Laboratory, located in Colorado, stores over 45,000 feet of ice cores that have been collected from 34 sites around the cryosphere.

Ice-core records reveal a historical correlation between increases in greenhouse gases and rises in global temperatures and sea levels. One major climate change occurred about 125,000 years ago, when a change in Earth's orbit increased global temperatures and released carbon dioxide from the oceans. During that event (which likely happened over thousands of years), temperatures rose by about seven degrees Fahrenheit, a large portion of Greenland's ice sheet melted, and sea levels rose over 10 feet.

The recent ice-core record shows that greenhouse gas levels are higher than they were at the last significant warming event 125,000 years ago. Greenhouse gas levels are the highest they have been in the last 500,000 years.

Evidence from ice cores indicates that human activity is causing climate change. In particular, the burning of fossil fuels is responsible for the extreme increase of greenhouse gas levels.